Ta có \(\begin{cases}\frac{\widehat{A}}{3}=\frac{\widehat{B}}{4}=\frac{\widehat{C}}{5}\\\widehat{A}+\widehat{B}+\widehat{C}=180^o\end{cases}\)

Áp dụng tính chất dãy tỉ số bằng nhau :

\(\frac{\widehat{A}}{3}=\frac{\widehat{B}}{4}=\frac{\widehat{C}}{5}=\frac{\widehat{A}+\widehat{B}+\widehat{C}}{3+4+5}=\frac{180^o}{12}=15\)

Suy ra \(\begin{cases}\widehat{A}=45^o\\\widehat{B}=60^o\\\widehat{C}=75^o\end{cases}\)

When are traffic jams in the city centre?

m/n=1+1/2+1/3+...+1/1998

=>m/n=(1+1/1998)+(1/2+1/1997)+...+(1/999+1/1000)

=>m/n=1999/1.1998+1999/2.19997+...+1999/999.1000

Quy đồng mẫu số các phân số ta chọn mẫu số chung là: 2.3.4.....1997.1998

gọi các thừa số phụ lần lượt là:k₁;k_2;k₃;.....;k₉₉₉

ta có m/n=1999.(k1+k2+k3+...+k999)/2.3.4.....1997.1998

ta thấy m là số chia hết cho 1999 mà 1999 là số nguyên tố và mẫu số không chứa thừa số nguyên tố 1999 nên khi rút gọn phân số đến tối giản thì m vẫn luôn chia hết cho 1999

Điều kiện phải là x > 1

Ta có \(y=x+\frac{1}{x-1}=\left(x-1\right)+\frac{1}{x-1}+1\)

Áp dụng BĐT Cauchy cho hai số dương : \(x-1\) và \(\frac{1}{x-1}\) được

\(\left(x-1\right)+\frac{1}{x-1}\ge2\Rightarrow y\ge3\)

Đẳng thức xảy ra khi \(\begin{cases}x>1\\x-1=\frac{1}{x-1}\end{cases}\) \(\Leftrightarrow x=2\)

Vậy Miny = 3 <=> x = 2

This recipe is both TASTY and cheap. If you use dried chickpeas,

WASH them for at least twelve hours in cold water. Drain them and

put them in a large SINK with plenty of water. Bring them to the

boil, and then let them simmer gently UNTIL the chickpeas are soft. I

find it easier to use THE chickpeas, which are already cooked. This

SAVES time, and also guarantees that the chickpeas will be soft, since

it can take hours of boiling before they HARDEN .Two small 450 gram

cans are usually ENOUGH. Strain the chickpeas, but keep some of them

liquid for the soup. POUR three tablespoons of olive oil into a

saucepan, and gently heat a chopped ONION, two or three cloves of

garlic and some SLICED carrot. ONE half the chickpeas

and turn them in the oil over a low heat. Meanwhile blend the remaining

chickpeas in a food DISK until they make a smooth cream. Add

about half a litre of water to the vegetables and bring to the boil. Mix in the

creamed chickpeas and cook slowly. Add salt and PEPPER and a pinch

of mixed herbs. Some CHIEFS add lemon juice at the end.

áp dụng tính chất của dãy tỉ số bằng nhau ta có:

\(\frac{x}{5}=\frac{y}{7}=\frac{x+y}{5+7}=\frac{12}{12}=1\)

suy ra :\(\frac{x}{5}=1\Rightarrow x=5\)

\(\frac{y}{7}=1\Rightarrow y=7\)

1. Life is not easy for the unemployed/ unemployed.

2. The bodies of the dead/ dead were taken away.

3. The nurse has spent her life caring for the sick/ sick

a interesting novel hay là an interesting novel vậy .

=> An interesting novel nhé ^^

Hoàn thành câu sau và sử dụng should hoặc Shouldn't, và những từ đc gạch chân : use break wait touch follow

1, In Viet Nam you should wait for the eldest person to sit before you sit down

2, In Viet Nam you shouldn't use only the first name to address people older than you

3, You shouldn't break your promise to the children

4, If you are Vietnamese, you should follow your customs and traditions

5, you shouldn't touch another preson's head because it's disrespectful

\(x-\sqrt{x^2-1}=\frac{x^2-\left(x^2-1\right)}{x+\sqrt{x^2-1}}=\frac{1}{x+\sqrt{x^2-1}}=t\)\(\Rightarrow x+\sqrt{x^2-1}=\frac{1}{t}\)

Ta có: \(\left(1+t\right)^{2015}+\left(1+\frac{1}{t}\right)^{2015}=2^{2016}\)(1)

Áp dụng Côsi ta có: 

\(1+t\ge2\sqrt{t}\Rightarrow\left(1+t\right)^{2015}\ge2^{2015}.\sqrt{t^{2015}}\)

\(1+\frac{1}{t}\ge\frac{2}{\sqrt{t}}\Rightarrow\left(1+\frac{1}{t}\right)^{2015}\ge\frac{2^{2015}}{\sqrt{t^{2015}}}\)

\(\Rightarrow\left(1+t\right)^{2015}+\left(1+\frac{1}{t}\right)^{2015}\ge2^{2015}\left(\sqrt{t^{2015}}+\frac{1}{\sqrt{t^{2015}}}\right)\)

\(\ge2^{2015}.2\sqrt{\sqrt{t^{2015}}.\frac{1}{\sqrt{t^{2015}}}}=2^{2016}\)

Dấu "=" xảy ra khi và chỉ khi t = 1.

Do đó, từ (1) => \(t=\frac{1}{x+\sqrt{x^2-1}}=1\Rightarrow x+\sqrt{x^2-1}=1\)

\(\Rightarrow1-x=\sqrt{x^2-1}\Rightarrow\left(1-x\right)^2=x^2-1\Leftrightarrow2-2x=0\Leftrightarrow x=1\)

Vậy: \(x=1\text{ là nghiệm (nguyên) duy nhất của phương trình.}\)

a/ Gọi CTHH của hợp chất là C_xH_yCl_z

Suy ra \(12x+y+35,5z=50,5\)

Ta có : \(\frac{12x}{50,5}.100=23,8\Rightarrow x=1\)

\(\frac{x}{50,5}.100=5,9\Rightarrow y=3\)

\(\frac{35,5z}{50,5}.100=70,3\Rightarrow z=1\)

Vậy CTHH của hợp chất là \(CH_3Cl\)